1. Field of the Invention
This invention is a tool bit intended for use in a metal cutting tool, in particular a tube end squaring tool.
2. Related Art
A typical tool bit useful in a tube end squaring tool such as described in U.S. Pat. No. 4,319,503 granted Mar. 16, 1982, includes a main body portion shaped by machining to present a cutting edge to a metal workpiece with an appropriate relief angle behind the cutting edge and a "hook radius" cut into the forward area of the cutting edge to present an entrance angle against which a chip separated from a metal workpiece flows during a cutting operation. A tool bit of this type is illustrated in the aforesaid U.S. Pat. No. 4,319,503.
Tool bits of this type are used for tube end squaring tools to machine the ends of tubes and pipes so they are square with the longitudinal axis of the tubular element and have a smooth and preferably burr-free surface at the end of the tubular element to prepare the element for a welding operation.
To achieve a smooth machined surface free of burrs, it has been found to be highly desirable to avoid heating the metal at the cutting zone to a minimum while promoting free flow of the cut metal chip away from the cutting edge of the tool bit. In accordance with prior art techniques, promotion of free chip flow includes polishing the hook radius leading away from the cutting edge and otherwise forming the hook radius area by machining procedures that maintain as smooth a surface as possible in the entrance angle area of the cutting edge of the tool bit. It is also conventional to provide a relatively high entrance angle for the cutting edge to keep burrs to a minimum, particularly if the metal being cut is relatively soft. Tool bits that are formed by grinding machinery are typically formed so that the grind lines run generally parallel to the cutting edge, and then another finishing operation is required to generate grind lines perpendicular to the cutting edge or to otherwise improve the finish of the entrance angle side of the cutting edge to reduce resistance to chip flow away from the cutting edge during a machining operation.
The various manufacturing and finishing operations required to produce an effective tool bit useful for a tube end squaring tool involves increased manufacturing and handling steps that in turn result in higher costs associated with manufacturing such tool bits. It would be highly desirable to reduce the manufacturing costs for such tool bits, the pricing of which is highly competitive in view of the expendable nature of the tool bits.
Specifically, it would be highly desirable if the entrance angle side of the cutting edge did not need to be highly polished or precision ground with the grind lines running perpendicular to the cutting edge, all of which contributes to the higher manufacturing costs of a tool bit useful for facing or squaring the ends of tubular workpieces.
Tool bits constructed in accordance with the prior art also exhibit "built-up-edge-cutting" (BUE cutting), which entails virtual welding of metal workpiece material to the cutting edge of the tool bit as cutting progresses, which reduces cutting efficiency, and, in the extreme, results in formation of a rough cutting edge comprising workpiece metal welded to tool bit stock. BUE cutting also may result in cyclic buildup of workpiece metal on the cutting edge and periodic sloughing off of the workpiece metal during machining, which also produces an irregular and burred surface.